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CELL Yr 1 > Membranes > Flashcards

Membranes Flashcards

1
Q

Give 5 properties of membranes

A 
Flexible
Self-sealing
Selectively permeable
They define the external boundaries of the cell
They divide the internal space
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2
Q

What are the majority of lipids in a lipid bilayer?

A

Phospholipids

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3
Q

What is cholesterol?

A

A large, flat molecule which is almost entirely hydrophobic, besides a hydrophilic OH group

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4
Q

Name 5 factors that affect membrane fluidity

A 
Temperature
Fatty acid composition
Chain length
Degree and extent of saturation
Cholesterol content
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5
Q

How does chain length affect membrane fluidity?

A

Longer fatty acid chains allow for more interactions and greater rigidity

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6
Q

How does degree and extent of saturation of fatty acids affect membrane fluidity?

A

Unsaturated fatty acids have kinks in their chains, meaning they can’t pack as closely together, so the membrane is less rigid and more fluid

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7
Q

How does cholesterol content affect membrane fluidity?

A

More cholesterol means more interference between inter-phospholipid reactions and more fluidity at low temperatures. More cholesterol holds the membrane together more at high temperatures, decreasing fluidity

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8
Q

How does temperature affect membrane fluidity?

A

At low temperatures, cholesterol interferes with reactions between phospholipids and increases fluidity. At high temperatures, cholesterol holds the membrane together and maintains its structure, decreasing fluidity

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9
Q

How does cholesterol disrupt interaction between fatty acyl chains?

A

Cholesterol hydroxyl groups form hydrogen bonds with the phospholipids and the hydrophobic tail disrupts the regular interactions between fatty acyl chains

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10
Q

How does spur cell anaemia affect cholesterol content and of what cells?

A

Spur cell anaemia can increase cholesterol content for lipid membranes of red blood cells by 25-65%, leading to decreased membrane fluidity. This deforms the membrane and makes it very rigid.

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11
Q

Why is spur cell anaemia referred to as a form of anaemia?

A

It’s referred to anaemia because the affected RBCs are much more fragile than healthy RBCs

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12
Q

How is lateral movement of lipids in the bilayer membrane different to transverse movement?

A

Lateral movement of lipids is rapid, while transverse movement is slow and requires the action of 3 enzymes

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13
Q

Where are membranes synthesised?

A

The endoplasmic reticulum

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14
Q

What happens before developing membranes move to the Golgi apparatus?

A

They undergo a degree of maturation

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15
Q

On what side of the ER are the enzymes responsible for the synthesis of new phospholipids present?

A

The cytosolic side

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16
Q

What transports some newly synthesised phospholipids from the cytosolic side where they’re made to the luminal side?

A

ABC transporter proteins (ATP-binding cassette transporter proteins)

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17
Q

Why is the movement of new phospholipids from the cytosolic side of the ER membrane to the luminal side active?

A

It requires ATP because it’s thermodynamically unfavourable as it allows the polar head group to pass through the very hydrophobic middle region

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18
Q

What do floppases do?

A

Floppases move phospholipids from the inner to the outer leaflet of the membrane

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19
Q

What do flippases do?

A

Flippases move phospholipids from the outer to the inner leaflet of the membrane

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20
Q

What do scramblases do?

A

Scramblases allow for bidirectional movement of phospholipids across the membrane

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21
Q

Why is apoptosis an important process in the body?

A

Apoptosis allows the body to turn over tissue without inducing an inflammatory response, allowing remodelling

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22
Q

What’s an important part of apoptosis that involves membranes?

A

Apoptosis involves significant changes in membrane structure. An important part of the process is redistribution of the phospholipids within a membrane, more specifically phosphatidylserine, which is found predominantly on the inner side of the membrane

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23
Q

Is apoptosis passive or active?

A

Active

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24
Q

What’s the important of the movement of phosphatidylserine to the outer surface of the membrane?

A

Phosphatidylserine in the outer surface of the membrane acts as an ‘Eat Me’ signal to phagocytes, primarily macrophages.

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25
Q

Why doesn’t apoptosis induce an inflammatory response?

A

The contents of the apoptotic cell are not spread into the extracellular space

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26
Q

What are integral membrane proteins?

A

Proteins that are intimately connected with the phospholipids by strong non-covalent bonds

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27
Q

Give 3 properties of integral membrane properties

A

They can be single or multi pass
They often have an alpha-helix transmembrane domain
They can be predicted from sequence

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28
Q

Give 3 properties of peripheral membrane proteins

A

They are more loosely associated with the membrane
They are located on the extracellular or cytosolic membrane
They are associated by non-covalent bonds

29
Q

How are lipid-anchored membrane proteins associated with the membrane?

A

They are covalently linked to a lipid molecule such as glycerol-phosphatidylinositol

30
Q

What percentage of membrane weight do membrane carbohydrates form?

A

2-10%

31
Q

In which direction do carbohydrates face on all membranes?

A

Carbohydrates face away from the cytosol

32
Q

What are membrane carbohydrates involved in?

A

Cell-cell interactions or cellular recognition

33
Q

What percentage of weight is carbohydrate in RBCs?

A

8%

34
Q

Describe membrane permeability to different molecules

A

Lipid soluble molecules can move bidirectionally through the membrane via concentration gradients and simple diffusion. Hydrophobic molecules and small uncharged or polar molecules can freely diffuse across a membrane, while large uncharged or polar molecules and ions cannot

35
Q

What does non-mediated transport involve?

A

A pore through the membrane for simple diffusion of capable molecules or a channel protein for facilitated diffusion

36
Q

When can non-mediated transport be active?

A

Never, its always a passive process

37
Q

Is carrier-mediated transport active or passive?

A

It can be either

38
Q

How can molecules be transported against their concentration gradient?

A

ATP is required, so it’s by active transport

39
Q

What are the 2 types of co-transporters?

A

Antiporters and symporters

40
Q

Why is carrier-mediated diffusion quicker than simple diffusion?

A

Simple diffusion rate is limited by the concentration gradient, while carrier-mediated facilitated diffusion rate is determined by the number of carrier proteins

41
Q

What type of transport does glucose use?

A

Carrier-mediated transport

42
Q

Where is GLUT 1 found and what’s it for?

A

GLUT 1 is found in all mammalian tissues fir basal glucose uptake

43
Q

Where’s GLUT2 found and what’s it for?

A

GLUT 2 is found in hepatocytes for removal of excess glucose from the blood and in pancreatic beta cells to play a role in regulation of insulin

44
Q

Where’s GLUT3 found and what’s its purpose?

A

GLUT3 is found in all mammalian tissues for basal glucose uptake

45
Q

Where’s GLUT4 found and how can the number of them be increased?

A

GLUT4 is found in muscle cells and fat cells. More transporters are introduced with endurance training

46
Q

Where’s GLUT5 found and what’s it for?

A

GLUT5 is found in the small intestine and is predominantly for fructose transport

47
Q

What characterises the kinetics of the GLUT transporters?

A

The Kt- the concentration at which the process is half its maximal value

48
Q

What does a low Kt mean?

A

Higher affinity of the transporter for its substrate

49
Q

Why does GLUT2 have a Kt of 15-20mM when GLUT1 has a Kt of 1mM?

A

GLUT1 is for constant uptake of glucose and at normal concentrations of glucose, GLUT1 is saturated. GLUT2 transporters are only meant to be active at raised glucose levels, to remove excess from the blood, so their Kt is above the normal glucose concentration so that they’re barely active at normal levels

50
Q

How do glucose transporters work?

A

They are huge, compact molecules that bind glucose, causing a conformational change that opens a pore to allow glucose to diffuse across the membrane, driven by its concentration gradient. This can be bidirectional.

51
Q

How is glucose concentration gradient between extracellular space and intracellular space maintained?

A

Glucose that moves into the cell is phosphorylated to glucose 6-phosphate for glycolysis, which keeps intracellular glucose concentrations low

52
Q

In what 3 ways are glucose transport kinetics similar to enzyme kinetics?

A

The transporters are specific to certain molecules. They exhibit saturation type kinetics. They can be regulated

53
Q

How can glucose uptake be regulated? Give an example

A

By increase in the number of transporters. Insulin stimulates the addition of GLUT4 transporters into the membranes of adipocytes and skeletal muscle cells to decrease blood glucose concentration

54
Q

Give an example of an important active transport process

A

Na+ ion concentration is around 10x greater outside the cell than it is inside, but there’s no free passive movement due to Na+ being an ion. Na+ K+ ATPase is an antiport pump that moves 3Na+ out of the cell against their concentration gradient for 2K+ moved in

55
Q

What can manipulate the Na+ K+ ATPase pump and how does it treat congestive heart failure?

A

Digitalis (digoxin) is an extract of fox glove which is a cardio tonic steroid that inhibits the Na+ K+ pump, resulting in increased intracellular sodium. This maintains intracellular Ca2+ concentration via the Na+ Ca2+ exchanger, so cardiac contraction is stimulated and congestive heart failure can be treated

56
Q

How is Na+ important to glucose transport?

A

There are sodium-dependent glucose transporters SGLUT-1 and SGLUT-2, which are co-transporters, or more specifically, symporters. They move sodium down its concentration gradient by facilitated diffusion, with glucose being carried with the Na+

57
Q

How is low Na+ concentration maintained within the cell to maintain the glucose symport?

A

Na+ K+ ATPase pumps move 3Na+ out of the cell for every 2K+ in. As the pump is active, although glucose uptake is passive, maintenance of the glucose uptake process is active as the Na+ K+ pump is essential to it

58
Q

How are transport proteins involved in cystic fibrosis?

A

Cystic fibrosis is a genetic disease for which 1 in 20 caucasians are carriers, with a single deletion at position 508. Individuals that carry the deletion in both copies of the gene produce a chloride channel protein that fails to insert into the membrane

59
Q

What is compartmentalisation?

A

The separation within a cell into sections based on function via membrane

60
Q

What does compartmentalisation in a cell do?

A

It separates reactions and enables the local environment to be regulated, for instance with pH. It brings together reactants responsible for carrying out a specific function.

61
Q

What is I-cell disease?

A

I-cell disease is classified as a lysosomal storage disease. Lysosomes have a pH of around 5.

62
Q

How is the low pH maintained in lysosomes?

A

The lysosome has a proton pump within its membrane. Following ATP hydrolysis, H+ ions are pumped into the lysosome to decrease the pH of the lysosome for optimal enzyme activity within the lysosome.

63
Q

What are the enzymes in the lysosome that need low pH?

A

Acid hydrolases

64
Q

What do acid hydrolases in lysosomes do under normal circumstances?

A

They break down a number of different molecules (complex carbohydrates, lipids etc.). The components can then be sent to different parts of the cell for further metabolism

65
Q

What is required to get the hydrolases to the lysosome?

A

A carbohydrate signal (a mannose residue added to the hydrolase). Under normal circumstances, the mannose is phosphorlyated and will direct the hydrolases to the lysosome.

66
Q

How is signalling affected in I-cell disease?

A

The enzyme that phosphorylates mannose is absent and so the hydrolase is not directed to the lysosome.

67
Q

What are the consequences of defected signalling in I-cell disease?

A

As a consequence, hydrolase ends up in circulation. This is how the disease can be diagnosed. Importantly, if the enzyme does not reach the lysosome, it cannot digest the molecules it should, so they accumulate within the lysosomes. Individuals with the disease die in early childhood

68
Q

Why does the inner mitochondrial matrix have very high relative protein content?

A

It houses all the components of the electron transport chain for oxidative phosphorylation

69
Q

How is the outer mitochondrial membrane structurally different to the inner membrane?

A

The outer mitochondrial membrane has less protein content because it’s not involved in oxidative phosphorylation directly, but instead acts as a barrier

CELL Yr 1 (13 decks)

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